Identifying real evidence in health & nutrition studies
Main goal of the study
Best practice (especially in RCTs): pre-register outcomes and analysis plan
Example (published RCT)
“We tested the hypothesis that long-term supplementation with omega-3 fatty acids would reduce cardiovascular events in this population.”
— NEJM, 2012
Population matters for relevance
Not all studies are done on humans, and not all humans are like you.
• Cross-sectional
• Prospective cohort
• Case-control
• RCT
• Pre–post (single-arm)
• Systematic review
• Meta-analysis
Observational
• Case-control – with vs without outcome
• Case report / series – detailed look at few patients
• Ecological – group-level data only
• Retrospective cohort – past records follow exposure → outcome
Mixed / Natural
• Longitudinal – same subjects over time
• Natural experiment – exposure assigned by external factors
Interventional
• N-of-1 trial – single participant, alternating treatments
• Cross-over trial – each subject receives all treatments
• Before–after study – compare pre- vs post-intervention
Synthesis
• Systematic review – structured summary, no pooling
• Umbrella review – review of systematic reviews
Power (1 − β): the probability of finding an effect if it really exists
Usual target: 80%
Grows with bigger N, larger effect, lower noise
What type of study is this: observational, interventional, or a synthesis?
Can this design support a causal claim, or only association?
Is the control / comparison group appropriate?
For meta-analyses, are the pooled studies similar enough?
Was the sample size justified, and did they report a power calculation for the primary endpoint?
Is this effect real? How exact is it?
| Concept | What it tells us | Quick example |
|---|---|---|
| Statistical significance (p-value) | Chance vs. real effect? | Supplement ↓ BP 5 mm Hg, p = 0.03 |
| Precision (95 % CI) | How exact is the estimate? | 5 mm Hg (CI −8 to −2) |
“5 mm Hg decrease, p = 0.03” → significant
| Finding (effect) | p-value | Interpretation |
|---|---|---|
| −0.15 kg (12 wk) | 0.001 | Statistically significant; clinically trivial |
| −8.5 mm Hg systolic BP | 0.09 | Not statistically significant; could matter if real |